West Nile Virus

What is the West Nile virus?

The West Nile virus is spread by mosquitoes. The West Nile virus can infect humans, birds, mosquitoes, horses, and some other mammals. Very rarely, the virus can spread in transfused blood, a transplanted organ, or through the placenta to a fetus.

West Nile virus occurs in mid- to late summer and early fall in mild zones. It can also occur year-round in southern climates. Most often, the West Nile virus causes no symptoms or a mild, flu-like illness. But the virus can cause life-threatening illnesses, such as:

Inflammation of the brain (encephalitis)

Inflammation of the lining of the brain and spinal cord (meningitis)

Inflammation of the brain and its surrounding membrane (meningoencephalitis)

What causes West Nile virus?

West Nile virus is spread to humans through the bite of an infected female mosquito. The mosquitoes get the virus when they bite an infected bird. Crows and jays are the most common birds linked to the virus. But at least 110 other bird species also have the virus.

West Nile virus isn't spread between humans. But in a few cases it has spread through organ transplant. Health officials think the organ donor acquired the virus through a blood transfusion. All blood is screened for the virus. The risk for getting West Nile virus from blood is much lower than the risk of not having any procedure that would call for a blood transfusion.

What are the symptoms of West Nile virus?

Most people infected with West Nile virus have no symptoms. They won't know they had the infection.

About 1 in 5 people who become infected will develop West Nile fever. This is a flu-like illness. These are the most common symptoms of West Nile fever:

Fever

Headache

Body aches

Skin rash on trunk of body

Swollen lymph glands

The more severe form of the West Nile virus affects mostly older adults. It occurs when the virus crosses the blood-brain barrier and can cause:

Headache

High fever

Neck stiffness

A state of impaired consciousness, extreme lethargy, and reduced reactivity to outside stimuli (stupor)

Disorientation

Coma

Tremors

Convulsions

Muscle weakness

Paralysis

These symptoms may look like other health problems. Always see your healthcare provider for a diagnosis.

Who is at risk for West Nile virus?

Certain things can increase the risk for getting West Nile virus. You are more likely to get the virus if you are exposed to mosquito bites during the summer months.

Most people who are infected have a minor illness and recover fully. But older people and those with weak immune systems are more likely to get a serious illness from the infection.

How is West Nile virus diagnosed?

Your healthcare provider will order a blood test to check for antibodies to the West Nile virus. He or she may also do a lumbar puncture to test cerebrospinal fluid for signs of infection.

How is West Nile virus treated?

Treatment will depend on your symptoms, age, and general health. It will also depend on how severe the condition is.

There's no specific treatment for West Nile virus-related diseases. If a person gets the more severe form of the disease, West Nile encephalitis or meningitis, treatment may include intensive supportive therapy, such as:

Hospital stay

IV (intravenous) fluids

Breathing machine (ventilator)

Prevention of other infections such as pneumonia or urinary tract infections

Nursing care

What are possible complications of West Nile virus?

Usually, the West Nile virus causes no symptoms or only mild, flu-like symptoms. But the virus can cause life-threatening illnesses, such as

Inflammation of the brain (encephalitis)

Inflammation of the lining of the brain and spinal cord (meningitis)

Inflammation of the brain and its surrounding membrane (meningoencephalitis)

Can West Nile virus be prevented?

At this time, there's no vaccine available to prevent West Nile virus. The CDC recommends taking these steps to prevent mosquito bites and West Nile virus:

Use insect repellent containing DEET (N,N-diethyl-meta-toluamide) when you're outdoors. If you spray your clothing, there's no need to spray repellent containing DEET on the skin under your clothing.

Consider staying indoors at dawn, dusk, and in the early evening. These are peak hours for mosquito bites, especially those mosquitoes that carry the West Nile virus.

Limit the number of places for mosquitoes to lay their eggs by getting rid of standing water sources from around your home.

Mosquitoes are drawn to people’s skin odors and the carbon dioxide you breathe out. Many repellents contain a DEET, which repels the mosquito. Repellents work only at short distances from the treated surface, so mosquitoes may still be flying nearby. Always follow the directions on the insect repellent to determine how often you need to reapply repellent. To boost your protection from insect repellent, remember:

Don't apply aerosol or pump products directly to your face. Spray your hands and then rub them carefully over the face, avoiding your eyes and mouth.

Repellents containing a higher concentration of active ingredient (such as DEET) provide longer-lasting protection. Read the directions to find out how long your product will last.

The American Academy of Pediatrics advises using care when putting insect repellent on children:

Use products with a low concentration of DEET, 30% or less, on children between ages 2 and 12. Some experts suggest that it's acceptable to apply repellent with low concentrations of DEET to infants older than age 2 months. For children younger than age 2, only one application per day of repellent containing DEET is recommended.

When using repellent on a child, apply it to your own hands and then rub them on your child.

Keep the repellant away from children's eyes and mouth and use the repellent sparingly around their ears.

Don't apply repellent to children's hands because children tend to put their hands in their mouths.

Don't allow a young child to apply his or her own insect repellent.

Keep repellents out of reach of children.

Don't apply repellent to skin under clothing. If repellent is applied to clothing, wash treated clothing before wearing again.

Always consult your healthcare provider for more information.

When should I call my healthcare provider?

Most people infected with the West Nile virus will have no or only mild symptoms. But if any of the following serious symptoms develop, seek medical care right away:

High fever

Severe headache

Stiff neck

Confusion

Muscle weakness

Vision loss

Numbness

Paralysis

Tremors

Seizures

Coma

Key points about West Nile virus

Humans get West Nile from the bite of an infected mosquito.

Usually, the West Nile virus causes no symptoms or only mild, flu-like symptoms.

The virus can cause life-threatening illnesses, such as encephalitis, meningitis, or meningoencephalitis.

There is no vaccine available to prevent West Nile virus. So it is important to avoid mosquito bites.

Next steps

Tips to help you get the most from a visit to your healthcare provider:

Know the reason for your visit and what you want to happen.

Before your visit, write down questions you want answered.

Bring someone with you to help you ask questions and remember what your provider tells you.

At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.

Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.

Ask if your condition can be treated in other ways.

Know why a test or procedure is recommended and what the results could mean.

Know what to expect if you do not take the medicine or have the test or procedure.

If you have a follow-up appointment, write down the date, time, and purpose for that visit.